Traveling conveyer system



Nov. 4, 1941. w. H. EMERSON 2,261,149

TRAVEIIING CONVEYER SYSTEM` Filed MaI-6h 12, 1940 2 sheets-sheet 1 17 1 Lv I L-@L I ll Y l :a h l dil* db l: f/ l. IgIIII-I 7 II IIII IIS.. I I II I I I I' I I: I I E III I I Ii I Iii II I I 'i I I iI I, II I: If III 'I II I I I I I: I I II I .I5 I EI II i I I EI I II E? III i I Ii I I: I. I I II IIII I I II/ I I II Il II I I :I II :l :I l l |L i' IIL Jn- I II II I' ,I I I I I I III I I III I I "I l' 'l l :'I 'l :l Il II III'I 1I I IIIIIIIII :II E I II II II I I .I II "I I I I I |JI II III II I II II |I I I I II III L-- I II II I I I 'II IA I 'I III 'I. II II i I IE I E I I 'III I II I II I ,II I I III II 5i II II I II I I I' .II aaa, l II La n :Il In s :i s! ,II III IIII' III Il 'I I I I 3'? -I I I I ,I. I I I 34 37 33 -I. f I JL I *H I :Iu-I 6 II 6 a II III I I II III II II i, iiII :"I I I: Ii I III I II-I I I Il I: I II I, l I II; I II 41 III I I I III. *I II "'0 62M III I I II I II 26 J- I fazIII I I I II L II :II II I II I! II; 3 50 y' III I| :I 'I II 0" I 'l Il :i I 3f 52 If I II III-II IIJ-f -lfEI-Z w/rNEJsfs -ma n 7,/ I /7/ INI/mon Mmm sa BY @Mw ya@ fm@ Wj' W Cu 4 ATTORNEYS.

Nov. 4;-, 19M. w. H, EMERSON v TRAVELING CONVEYER SYSTEM 2 Shets-Sheet 2 Filed March 12, 1940 INVENTR.

WITNEJSE.

A ATTORNEY@ is driven by suitable means.

Patented Nov. 4, 1941 2,261,149 TRAVELING CONVEYER SYSTEM l Walter H. Emerson, East Liverpool, Ohio, assign-'- or to The Homer Laughlin China Company, Newell, W. Va., a corporation of Delaware Application March 12, 19411seria1 No. 323,542

` 16 claims. (o1. 19a-116)y This invention relates to endless 4conveyers, and more particularly to those of relatively great length.

With endless conveyers of great length, such,

for example, as those used for transporting pottery-ware through a drier, difficulty is experienced in starting the conveyer in motion due to its great weight and extremely high starting friction. If anything happens to increase the running friction of such a conveyer materially, or to stall the conveyer while the driving means is still operating, the conveyer may be broken;

Itis among the objects of this invention to provide an endless conveyer system which can easily be started in operation with relatively small power under normal conditions, regardless of the length Iof the conveyer; which indicates at all times the amount of pull exerted on it; which automatically shuts olf its driving means in case of emergency; which automatically picks up and deposits articles at desired points; and which. includes readily interchangeable article carriers.

In accordance with this invention an'endless conveyer is supported by rotatable membersand provided between two of the rotatable members near the tension side' of the driving means with a loop, by which is meant any slack in the conveyer, and to which is connected means for normally holding the loop in a predetermined position. This loop-holding means exerts less tension on the loop than is required to overcome the starting resistance of the major portion of the conveyer which is behind the loop;v that is, between the loop' and the slack side of the driving means. However, means is provided for gradually'increasing the tension on the loop as the loop isshortened when the driving means is started in operation until 'the pull "on the conveyer is sulicient to overcome ythe starting resistance of itsf 'major portion.l In this way the driving means is permitted to gather speed and momentum while merely exerting enough pull to shorten the loop, whereior4 the pull necessary to overcome the starting resistance of. the major portion of the conveyer is built up gradually by the driving means.

The shortening loop causes a series of electric switches to be actuated which are connected to,

means for indicating the amount of pull on the conveyer at any time. In a similar way an 'electric switch is actuated when the pull on the conveyer approaches the danger point, due to an abnormal increase in the running friction, for shut- The conveyer is .y

ting oi the driving means. Preferably, means is also connectedto the conveyer adjacent the slack side ofk the driving means for taking vup slack in the conveyer, which always occurs when the 4driving means is first started in operation and before the major portion of the conveyer starts to move.

The conveyer preferably comprises an endless chain supported by sprockets and carrying laterally projecting article carriers `which are pivoted thereto so that they will always hang horizontally. The article-engaging portion of each carrier may lbe made readily detachable', from the remaining portion so that article-engaging portions of different sizes can beinterchanged. At the loading station for the conveyer the article carriers pass upwardly through recesses in article-supporting means whereby the carriers pick up the articles.

These articles may be deposited Vat a desired point by moving loaded carriers downwardly through recesses in receiving means. Y

The preferred embodiment of the invention is illustrated in the accompanying drawings, in which Fig. 1 is a side view of my conveyer passing through a drier housing the side wall of which is partly broken away; Figs. 2 and 3 are enlarged. fragmentary vertical transverse sections taken on the lines II-II and III-III, respectively, of Figs. 1; and Figs. 4, 5, 6 are enlarged plan, side and end views, respectively, of a cou- 'ple of the article carriers that are attached to the conveyer. chain; and Fig. 7 is a wiring diagram of the electric switches and pull-indicating lights.

Referring to Fig. 1 of the drawings, my conveyer is shown in use in a pottery plant for transporting dinner-ware from an automatic wareforming machine l, such as shown in my cepending application Serial No. 328,638, filed April 9, 1940, through a drier 2 to an unloading stationA 3, and for conveying vthe emptied molds 4 backgto the machine. Molds 4 are shown only in Fig. 5, but it should be understood that when the conveyer is used in a pottery plant there is such a mold on every conveyer ring 56, and dinnerware is formed on the molds at machine I and stripped therefrom at station 3. Of course, the use of this conveyer is not coniined to pottery plants.

The drier comprises a structural steel frame 6 enclosedby suitable panel members 1 to form a l housing that is divided into sections separated v'from each other by parallel vertical partition walls 8` (Figs. 2 and 3). The hot air by which the ware is dried is drawn through the housing from end to end'by suction apparatus (not shown), connected to one end of it. The purpose of partitions 8 is to form baies for directing the hot pending upon the number of machines I servedv by the drier. Half of one of these double machines is shown in Fig. 1, it being understood that there are two more double machines mounted at the right of the one shown. ASuspended from transverse beams I8 above the floor I9 of the housing is an intermediate series of sprockets 2| staggered longitudinally of the housing relative to the upper sprockets, and mounted on the housing support below its iioor isa lower series of sprockets 22. In the section of the housing at its entry or yright-hand end, the intermediate sprockets 23 and 24 and a portion 29 of the housing floor are mounted at a higher level than sprockets 2| and floor I9, the end sprocket 23 being suspended from cross beams 26 supported by beams 21, and the central sprockets 24 being movable vertically for a purpose to be described presently,

An endless conveyer chain 28, extending upwardly from a drive sprocket 29 driven from ware-forming machine I, passes over a sprocket 30 journaled on a framework 3l extending horizontally away from the end of the drier housing. The chain enters the housing through an Vopening in its end wall, passes under the first sprocket 23, up through floor 20 to the rst top sprocket I1, kdown to sprocket 24,11p to the second top sprocket and so on in this manner until it reaches the last section of the housing. The chain there travels over two top sprockets in succession and then downwardly to form a loop before it passes over the top of an intermediate sprocket 32 and horizontally out of the housing. Sprocket ,32 is mounted on a framework 33 projecting from the end of the drier housing and supporting at its -outer end other sprockets 34 around which the two outer chains travel downwardly past `the unloading station 3 and through the building floor 35 to sprockets 36 under which they pass back to lower sprockets 22. The center chain passes downwardlyfrom a sprocket 31 on framework 33 to a sprocket 38. As vthe three chains pass the unloading station the dried ware is stripped from the molds before they .are returned to the wareforming machine. 1

The chains are `supported 4by lower sprockets 22 as they travel back beneath housing iioor I9 until they reach sprockets -39 in the iirst section of the housing. They then pass upwardly around .these sprockets and out of .the housing over sprockets 4-I, and the .near chain travels down around a sprocket 42, supported by framework 3|, to drive sprocket 29. The other two chains travel farther out along framework 3| before passing down over sprockets (not shown) to their respective machines.

As shownin Figs. 4 to v6, each conveyer chain is formed from single straight links I pivotally mounted at their ends between the ends of double straight links .52 which receive the teeth of the various sprockets. It is a feature of this invention that, extending Vtransversely through the center of every other single link, there is a pin 53 on the opposite ends of which the upper ends of brackets 54 are pivotally mounted. Rigidly connected to the lower end of each bracket is a laterally projecting arm 55 on the outer end of which there is a horizontal ring 5B for lifting loaded molds 4 from recesses in the turntable 5'! of the ware-forming machine and carrying them through the drier and back empty to the machine. Brackets 54 are adapted to cooperate with guide members (not shown) adjacent the machine and the unloading station to prevent the mold carriers from swinging at those points.

Each mold carrier may be a unitary device or it may be made in such a way that carrier rings of different sizes are interchangeable with the bracket. In the latter case the arm 55 is divided into two parts, as shown in Fig. 4, one attached to the bracket and the other to the ring. The adjoining ends of the arms have longitudinally overlapping portions provided with transversely aligned openings only one of which extends entirely through its portion of the arm. A pin 58 is removably disposed in the openings to prevent the two parts of the arm from separating axially of the arm, and a sleeve 59 encircles the arms overlapping portions to prevent them from. separating in any other direction. The sleeve, which is slidably mounted on the arm, is pressed tightly against the projecting end of pin 58 by a coil spring B0 encircling the arm between the sleeve and bracket.

It will be realized that the resistance of such a large conveyer to starting is very great. This is due to the starting friction of the sprockets and to the great weight of the long conveyer to which must be added the weight of the molds and the ware carried by them. A motor powerful enough to overcome this starting resistance in the usual way would have very much more power than is required to drive the conveyer after it has been set in motion, and the tremendous pull or tension suddenly exerted upon the chain by such a motor might be more than the chain and drier housing could stand unless they were made exceedingly strong, which would greatly increase their cost.

In accordance with this invention these difficulties are avoided by providing means for allowing the driving means and a relatively short section of the conveyer to get in motion and to gradually gather speed and momentum before the main portion of the conveyer is moved. Accordingly, as shown in Figs. l and 3, supported by each chain loop suspended in the last section of the housing is a sprocket 62 pivoted in the upper ends of a pair of vertical side bars 63 that support between them a weight 64 which is just heavy enough when the conveyer is running and operating normally to hold the loop extended suiiciently for the weight to rest on cross beams 65 supported at their ends by beams 66. Projecting from the outer face of each side bar near its top and bottom are guide brackets 61 that are slidably mounted in vertical guide members 63.

As the starting resistance of the portions of the conveyer between the driving sprocket 29 and the loop in the last section of the drier housing is .considerably less than the starting resistance of the much longer portion of the conveyer in the housing behind the loop, only enough power need be `applied to start the former portion of the conveyer because the loop permits that portion to get under motion without moving the rest of the conveyer. That is, the great resistance of the major portion of the conveyer to starting causes the last upper sprocket I1 in the -drier housing to serve; temporarily as a stationary point or anchor for the rear end of the loop, so rthat las soon as.Y the forward portion of the conveyer starts moving it raises or shortens the loop, weight 64 rising with it, instead of immediately setting the rest of the conveyer in motion. Howevezg while'the weight is rising, during the time that the driving motor for sprocket 29 is getting? up to speed, the weight exerts a gradually increasing downward pull on the loop, preferably because of a pairoof parallel weighted rollers 1I. These are suspended from the main weightvby-a pair of links I2 pivotally connected to the opposite ends of each roller, the other ends of theV links being pivoted to the lower ends of a pair of vertical links 'I3 whose upper ends are pivoted to the bottom of the main weight.

The rollers are supported by and roll upon upwardly curved concave tracks 'I4 so that as 'they are pulled toward each other by the rising weight they simultaneously move upwardly on o the tracks whose inclination gradually increases until it is vertical, at which point practically the entire weight of the rollers would be carried byl main weight 64. Consequently, it will be seen that as these rollers are drawn upwardly they gradually increase the weight on the loop until Ythe pull on the chain reaches and exceeds the quired to keep the conveyer running is a great Y deal less than that required to start it.

To take up any slack that may occur in the chain, and which always does tend to 'occur on the slack side of the driving sprocket 29 between it and sprocket 30 when the former is first started in operation and the portion of the chain directly ahead of it in the drier housinghas not yet started to move, a weight 76 (Fig. 2) is suspended from the vertically movable sprocket 24 in the iirst section of the housing. Like weight 64 at the opposite end of the housing, weight 16 is supported by vertical side bars 11 inthe upper ends of which sprocket 24 is pivotally mounted. Projecting from the outerface of each side bar near its top and bottom are guide' brackets 18 that are slidably mounted in vertical guide members 79 extending downwardly from a cross beam 26. Weight 16 pulls sprocket 24 downwardly when driving sprocket 29 rst starts to rotate, but it is raised by sprocket 24 as soon as the entire conveyer begins to move and to take up the slack.

Another feature of this invention is that the conveyer automatically indicates the amount of pull on the chain at all times, and stops itself whenever that pull tends to become excessive by reaching a predetermined amount. This is accomplished by means including a series of vertically spaced electric switches 8l that may be attached to the side of a guide member 68 of the chain pull mechanism. Projecting laterally from the side of weight 64 is an actuating member 82 which closes each switch in succession as the weight is raised by the shortening loop. The switches are connected in circuit with indicating means located in a convenient position, such as a series of lights 83 mounted on the ware-forming machine I. Opposite each light there is a number indicating the number of pounds pull on the chain that is required to lift the weighted high 7 5 enough toy causeactuating member 82 to close the'switch connected to the light in question.'

Y` These 'lights are of no particular value when ltheconveyer is iirst started in operation because `it islexpected'that the weight will rise to a considerable height kat that time.

However, after thev `entire conveyer vhas been set in motion the 'weight is supposed to drop back toits original position on beams 65. Thereafter, if one or more of the indicating lights 83 is illuminated it is Va sign'that Vthe weight is 'rising again, which` means that the running friction of the conveyer 'has been increased above normal and has correspondingly increased the pull on the chain. In y 'such a casethel lights are a signal to the attendant Athat something is wrong with the conveyer, such as a sticking sprocket, rfouled chain or the like, andshouldb'e investigated.

if If the diiculty is so serious as to stop the chain, weight 64'is raised far enough to close the top switch 8| which is connected to a relay `84 or the like (Fig. 7) that opens the electric circuit tol th'e motor 85 that drives driving sprocket '29; .-'Thisftop switch is located low enough on 'guide member V68fto permity the weight to be drawn upwardly a little further by the coasting :chain after the driving means has been shut oi, whereby the Vchain'drive and chain are stopped before the pull on the chain becomes great enough tovbreak the chain.` y l According tothe provisions of the patent stat- Vutes; I have explained the principle and Inode Yof operation `of my' invention Vand have illustrated anddescribed `what I now consider to 'represent 'q its best embodiments. desire to have! it `vunderstood that, within `the However, I

scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described. f

lA traveling conveyer system' comprising an "endless conveyer, means for drivingthe conveyer, spaced members Asupporting the conveyer with a loop between? two Aof said members adjacent the tension sidefof said driving means, and means connected Yto the loop for normally holding it in 'a predetermined position but normally exerting l/m'at'erially less tension on theloopthan required to overcome the starting resistance of the portion of the' conveyer behind the loop whereby the' loop` starts to rshorten when said driving 'means 'starts operating, said loop-holding means 'being 'adapted to increaseits load on the loop as vthe loop'becomes shorter until the increasing t'ension is suflicient to overcome said starting resistance." v l `2. A traveling conveyer system comprising an i'endless conveyer, means for driving the'conveyer. krotatable means supporting the conveyer with a loop" between two of said means adjacent the tension side of said driving means, a rotatable whereby the loop starts to shorten when said :driving meansstarts operating, the pull means beingadapted to increase its pull on said loop as the loop becomes shorter until the increasing pull is suicient' to overcome said starting reosistance.y

3. A traveling conveyer system'comprising an endless conveyer, means for driving the conveyer,

:a `portion of the conveyerhaving material resistance to starting in motion, a pair of rotatable members supporting the conveyer between said portion and the tension side of said driving `means-the conveyer forming a loop between said members, a rotatable member supported by said loop, pull means connected tothe last-mentioned member for normally holding said loop in a predetermined position, and tension `means connected to the conveyer between said conveyer portion and the slack side of said driving means for taking up slack in the conveyer, said pull means normally exerting less pull on the loop than required to overcome said starting resistance and being adapted to exert an increasing pull on said loop as the loop shortens when said driving means is started in operation, whereby the driving means gathers momentum while shortening the loop until the increasing pull on the loop is suicient to overcome said starting resistance. y l

4. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a loop between two of said means adjacent the l tension side lof said driving means, a rotatable member supported by said loop, a weight connected to said member for normally holding said loop in a predetermined position but normally exerting less pull on the loopA than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby the loop ,starts to shorten when said driving means starts operating, and means for increasing the pull of said weight on the loop as weight is raised by the shortening loop until the increasing pull on the loop is suicient to overcome said starting resistance.

5. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a 4loop between two of said means adjacent the -as weight is raised by the shortening loop until the increasing pull on the loop is surcient to overcome said starting resistance.

6. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a loop between two of said means adjacent the tension side of said driving means, a rotatable member supported by said loop, a main weight connected to said member for normally holding said loop in a predetermined position but normally exerting less pull on the loop than required to overcome the starting resistance ofthe portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, an auxiliary weight disposed below said main weight and connected thereto, and an upwardly curved concave track supporting said auxiliary weight whereby the downward pull of the auxiliary weight on said main weight .increases as the auxiliary weight is pulled up the increasinglysteep'track by the shortening loop until the increasing pull on the loop is sufcient to overcome said starting resistance.

'7. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a loop between two of said means adjacent the tension side of said driving means, a rotatable member supported by said loop, a weight connected to said member for normally holdingvsaid loop in a predetermined position but normally exerting vless pull on the loop than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, a cylindrical weighted roller disposed below said weight, means rotatably connecting-said roller to the weight, and an upwardly curved concave track supporting the rollerwhereby the downward pull of the roller on said weight increases as the roller is pulled rup the increasingly steep track by the shortening loop until the increasing pull on the loop is suiiicient to overcome said starting resistance.

8. A traveling conveyer system comprising an upper and a lower row of spaced rotatable members, an endless `conveyer having its upper portion supported by the upper rotatable members and extending downwardly between them around the lower rotatable members to form generally vertical strands, the lower portion of the conveyer Vextending laterally below said lower row of rotatable members, means operatively connected to the conveyer for driving it, one of Asaid lower rotatable'members adjacent the slack side of the driving means being vertically movable, a weight supported by said vertically movable member for taking up slack in the conveyer, one of said rotatable members adjacent the tension side of the driving means being vertically movable, a weight supported by said last-mentioned member, a cylindrical weighted roller disposed below said weight, means rotatably connecting said roller to the weight, and an upwardly curved concave track supporting the roller whereby the downward pull of the roller on said weight increases as the roller is pulled up the increasingly steep track by the shortening loop until the increasing pull on the loop is sufficient to overcome the starting resistance of the upper portion of the conveyer between said vertically movable rotatable member.

9. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a loop between two of said means adjacent the tension side of said driving means, a rotatable member supported by said loop, pull means connected to said member for normally holding said loop in a predetermined position but normally exerting materially less pull on the loop than required to overcome thestarting resistance of the portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, the pull means being adapted to increase its pull on said loop as the loop becomes shorter until the increasing pull is suicient to overcome said starting resistance, and emergency means actuated when said loop is shortened a predetermined amount for stopping said driving means.

10. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a loop between two of said means adjacent the tension side of said driving means, a rotatable member supported by said loop, pull means connected to said member for normally holding said loop in a predetermined position but normally exerting materially less pullv on the loop than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, the pull means being adapted to increase its pull on said loop as the loop becomes shorter until the increasing pull is sufficient to overcome said starting resistance, and means actuated as the loop shortens for indicating the amount of pull on the conveyer.

11. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a loop between two of said means adjacent the tension side of said driving means, a rotatable member supported by said loop, a weight connected to said member for normally holding said loop in a predetermined position but normally exerting less pull on the loop than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, means for increasing the pull of said weight on the loop as weight is raised by the shortening loop until the increasing pull on the loop is suicient to overcome said starting resistance, and an electric switch actuated by said weight when it rises a predetermined amount for stopping said driving means.

l2. A traveling conveyer system comprising an endless conveyer, means for driving the conveyer, rotatable means supporting the conveyer with a loop between two of said means adjacent the tension side of said driving means, a rotatable member supported by said loop, a weight connected to said member for normally holding said loop in a predetermined position but normally exerting less pull on the loop than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, means forv increasing the pull of said weight on the loop as weight is raised by the shortening loop until the increasing pull on the loop is suiiicient to overcome said starting resistance, a plurality of vertically spaced electric switches actuated in succession by said rising weight, and means controlled by said switches for indicating the amount of pull on the conveyer.

13. A traveling conveyer system comprising an endless chain, a plurality of sprockets supporting the chain, means for driving the chain, said chain being provided with a loop between two of the spockets adjacent the tension side of the driving means, a rotatable member supported by said loop, a plurality of article carriers pivotally connected to the side of the chain, and pull means connected to said rotatable member for normally flo holding said loop in a predetermined position but normally exerting materially less pull on the loop than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby Athe loop starts to shorten when said driving means starts operating, and the pull means being adapted to increase its pull on said loop as the loop becomes shorter until the increasing pull is sufficient to overcome said starting resistance.

14. A traveling conveyer system comprising lan endless chain, a plurality of sprockets supporting the chain, means for driving the chain, said chain being provided with a loop between two of the sprockets adjacent the tension side of the driving means, a sprocket supported by said loop, a plurality of brackets pivotally connected at their upper ends to the side of the chain, an arm connected to the lower end of each bracket and projecting laterally therefrom, means connected to the outer end of each arm for supporting an article, and pull means connected to the lastmentioned sprocket for normally holding said loop in a predetermined position but normally exerting materially less pull on the loop than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, the pull means being adapted to increase its pull on said loop as the loop becomes shorter until the increasing pull is suflicient t0 overcome said starting resistance.

15. An article carrier for an endless traveling chain comprising a. bracket adapted to be pivotally connected at its upepr end to the side of the chain, an arm projecting laterally from the lower end of the bracket, a horizontal ring connected to the outer end of the arm, said arm being divided into two parts having longitudinally overlapping portions provided with a pair of transversely aligned openings, a pin removably disposed in said openings and projecting therefrom, a sleeve encircling said overlapping portions, and a coil spring encircling the arm and biasing the sleeve against the projecting end of the pin.

16. Apparatus for aiding in starting a traveling endless conveyer having a loop between two of its supporting means adjacent the tension side of its driving means, said apparatus comprising means connected to said loop for normally holding the loop in a predetermined Aposition but normally exerting materially less tension on the loop than required to overcome the starting resistance of the portion of the conveyer behind the loop whereby the loop starts to shorten when said driving means starts operating, and means for increasing the pull of said loop-holding means on said loop as the loop becomes shorter until the increasing tension is suii'icient to overcome said starting resistance.

WALTER H. EMERSON. 

